This research aims to characterize the speech production of postlingually deafened adults before and after they receive cochlear implants, in order to contribute to our understanding of disordered speech in deafness and the role of hearing in normal speech. Our findings to this point indicate significant deterioration of speech parameters in postlingually deafened adults and, following activation of their cochlear implants, substantial longitudinal changes, often, but not uniformly, in the direction of normalcy. The theoretical framework of our research provides that articulatory movements are programmed to achieve sequences of feature- specified articulatory and acoustic goals. This programming uses an acquired internal model of relations between articulatory commands and acoustic output; we term the parameter settings of this internal model the phonemic settings. With some hearing restored with a cochlear prosthesis, speakers change phonemic settings (reflected in, e.g., vowel F2, sibilant spectra) at the same time they make postural adjustments (e.g., reflected in such changes as average SPL, rate, FO). To develop and evaluate this theoretical framework, we propose conducting three kinds of experiments; (1) long-term, longitudinal studies of speech before and after implantation; (2) short-term studies, in which signals from the implant are modified or interrupted or, with hearing subjects, in which auditory feedback is temporarily altered; and (3) perceptual experiments, in which implant users identify phonemes and discriminate synthetic speech stimuli, and in which their intelligibility is evaluated by normally-hearing listeners. The experiments focus mainly on: three spectral contrasts (vowels, sibilants and plosives), a timing contrast (plosive voicing), coarticulation, variability of phoneme targets, and suprasegmental regulation of FO and SPL. We will test predictions derived from the theoretical framework; e.g., postural changes are more rapid than phonemic resettings; implant users will be able to discriminate those contrasts that they change pre- to post-activation; access to auditory validation of phonemic settings will reduce variability around phoneme target values; phoneme contrasts produced with access to self-hearing are more intelligible than those produced without it. The body of knowledge concerning the speech of implant users provides some information on "speech benefit" from the cochlear implant. Our findings also bear on broader theoretical issues in speech science, such as the articulatory underpinnings of disordered speech, especially in deafened adults; interrelations among speech parameters (linkages) in the speech of deafened adults and in speakers with normal hearing; the role of prosthetic hearing in determining the characteristics of implant-user speech; the role of hearing in articulatory programming in speakers with normal hearing.